As disclosed in JP 2011-244682 A (corresponding to US 2011/0282513 A1), a system including electric devices of a residence uses a vehicle battery or charges the vehicle at a most appropriate time in order to adjust a balance between supply and demand of electric power.
In order to use the vehicle battery appropriately in an adjustment of the balance between supply and demand of electric power, a utilization plan of the vehicle battery needs to be created. The utilization plan of the vehicle battery is created based on a system state at a present time and a predicted balance between supply and demand of electric power in the future. This is because, an optimum value in the utilization plan during a limited time scale is not always equal to an optimum value in the utilization plan during a long-term time scale. In this case, information indicating whether the vehicle battery is to be connected to the system in the future with respect to the present time needs to be acquired in advance. Suppose that the information is acquired only by an input operation performed by a user. In this case, the utilization plan of the vehicle battery cannot be properly created when the input operation is not performed by the user or the information input by the user is not updated.